Electronic instrumentation can become inoperable due to the moisture in the air condensing within the instrument housing, causing corrosion within the electronic circuitry and possible shorting between the electronic components. This problem is of particular concern for electronic instrumentation used in humid, jungle type environments having warm days and cool nights, or carried through mountainous regions which exposes the instrument to changing pressures and temperatures. The condensation within an instrument is typically caused by an increase in pressure or decrease in temperature about the instrument.
One possible solution to eliminate this problem is to hermetically seal the instrument so as to attempt to prevent moisture from entering the housing. This solution, however, has been found to still have problems since no seal is perfect. Changes in pressure or temperature will cause even a hermetically sealed housing to expand and contract creating an intense force on the seal and eventually allowing air and the accompanying water vapor to seep into the container. Although some of this air and moisture will be exhausted as the instrument is exposed to lower temperatures, some condensation of the vapor will still occur within the instrument. This condensation becomes accumulative as the container expands and contracts over a period of time. The hermetic seal can in itself become a problem due to periodic maintenance or calibration cycles that require the intermittent breaking of the seals thereby weakening its ability to provide a proper seal. Further, there is always the possibility of aggravated situations due to improper reinstallation of the seal. Additionally, exposure to constant humidity and heat can cause the seals to deteriorate at much faster rates requiring the frequent replacement of the seals in order to prevent accumulation of water vapor into the instrument.
Although moisture filtering devices have been previously disclosed for use with electronic instruments, none of the prior art filters have been concerned with the needs associated with the portability and interchangeability associated with electronic instruments such as radio frequency transceivers. Usually these radio frequency units are rack mounted, self-contained units that automatically connect to electrical connectors and require a minimum number of other connections for quick and simple replacement. An example of a filtering device for controlling humidity in electronic equipment of the prior art is the U.S. Pat. No. 3,906,798, which discloses a filter adapted for use with instrumentation in aircraft, wherein the instrument was located in a panel and the filter located external to the instrument separately connected thereto. Such devices are not readily adaptable to portable equipment such as radio transmitters and receivers which are either hand carried or rack mounted in a vehicle. The need for portable electronic equipment to be as compact as possible requires a filtering device to extend within the instrument. Any extending filtering device would hamper the instrument's installation and mobility.